1. Field of the Invention
The Improved Wheel can be used in various applications, including but not limited to trash containers, lawn mowers, toy wagons, and the like. The Improved Wheel is a semi-pneumatic design and is manufactured using a two step process. In the first step, disc-shaped interlocking hubs are produced using conventional injection molding techniques from a thermoplastic, such as, but not limited to, high density polyethylene (HDPE) or a thermoset plastic such as polyphenaline sulfide (PPS). In the second step, a pair of the aforementioned disc-shaped interlocking hubs are inserted in opposing positions of the open mold in a conventional blow molding machine which then produces the Improved Wheel. The tube and web of the Improved Wheel are preferably formed from an elastomer such as Santoprene.RTM. thermoplastic rubber; however, various thermoplastics may also be suitable.
2. Description of the Prior Art
The Assignee of the present invention, Semco Plastic Company, Inc., manufactures a variety of products using conventional injection molding and blow molding techniques. Semco manufactures a number of wheels which are blow molded from HDPE. These wheels will not support a significant load nor or they intended for applications that will see a substantial amount of travel. The most common application for these blow molded HDPE wheels is for outdoor grills.
Semco and others in the industry use various types of inserts in connection with blow molding of these HDPE wheels. The most common type of insert is a circular white ring which is used to create a white sidewall in the black wheel. This technique uses a two step manufacturing process. In the first step, the white ring is injection molded from HDPE. In the second step, the white ring is manually inserted inside one half of the open mold of a conventional blow molding machine. The parison is then extruded between the open halves of the mold in the conventional blow molding machine. When the two halves of the mold close and capture the parison, the white sidewall sticks to the hot parison and forms an integral part of the black wheel. This white sidewall insert is strictly ornamental and does not enhance the strength of the HDPE wheel.
Use of various other inserts in blow molding is known to those skilled in the art. U.S. Pat. No. 4,664,958 entitled "Hollow Plastic Container Having An Insert" discloses an insert which is used in connection with blow molding of large drums. The insert, which is a threaded bung, could be plastic or metal. U.S. Pat. No. 3,919,374 entitled "Method For Blow Molding A Container Having An Auxiliary Component Formed As An Integral Part Of It" likewise teaches use of an insert in connection with the manufacture of a container. The insert which is identified as a plug is placed into the cavity of an open mold prior to extrusion of the parison.
Other inserts have been used in various blow molding processes. See for example: U.S. Pat. No. 4,991,878 entitled "Method For Producing A Blow-Molded Body"; U.S. Pat. No. 5,000,904 entitled "Device And Process For Production Of A Blown Three-Handled Container"; U.S. Pat. No. 4,674,759 entitled "Trash Container Wheel Structure"; U.S. Pat. No. 4,031,937 entitled "Unitary Tire-Wheel" and U.S. Pat. No. 3,062,254 entitled "Molded Wheel Having Internal Reinforcing."
The general use of inserts is also known in the field of injection molding. U.S. Pat. No. 4,040,670, entitled "Method Of Molding A Skate Wheel Having A Polyester Core And A Polyurethane Case And The Product Thereof" teaches the use of a rigid core which is surrounded by a clear wear resistant wheel casing.
There are several other patents dealing with solid core and semi-pneumatic type wheels which address some of the common interlocking problems associated with wheels of this type. These various patents are listed in the Information Disclosure Statement filed concurrently herewith.
The present invention includes opposing interlocking hubs which capture and adhere to the parison during the blow molding process. The Improved Wheel has and wear characteristics when compared with conventional HDPE wheels. Because of the economics of blow molding, the Improved Wheel is more economical to manufacture than conventional solid core wheels.